1. Field of the Invention
The invention relates to a power output apparatus, a vehicle on which the power output apparatus is installed, and a method of controlling the power output apparatus.
2. Description of the Related Art
A conventional power output apparatus includes an engine; a fuel tank in which fuel that is supplied to the engine is stored; a canister that traps fuel vapor in the fuel tank and allows the trapped fuel vapor to be purged into the intake pipe of the engine; an electric motor that generates power to drive a drive shaft; a planetary gear that is connected to three shafts, i.e., the output shaft of the engine, a drive shaft and a rotary shaft, and is arranged to transfers power between the three shafts based on power received from or supplied to two of the three shafts; and a generator that generates electric power using the power received from the rotary shaft of the planetary gear. The power output apparatus of this type performs so-called purge control by causing the canister to trap fuel vapor generated in the fuel tank, and purging the fuel vapor trapped in the canister, along with outside air, into the intake pipe, utilizing a negative pressure in the intake pipe. In a hybrid vehicle as described in Japanese Patent Application Publication No. 6-233410, when the weight of the canister exceeds a prescribed weight while the engine is at rest, and the vehicle is running, the engine is operated to carry out purge control to appropriately dispose of the fuel vapor trapped in the canister.
When the absolute value of the intake manifold negative pressure is equal to zero or close to zero, such as when the throttle valve of the engine is fully open, only a small amount of purge gas (a mixed gas of fuel vapor trapped in the canister and outside air) flows into the intake pipe, even if a purge control valve provided in a purge passage connecting the canister with the intake pipe is fully opened. Therefore, when a large amount of fuel vapor are trapped in the canister, it unfavorably takes a long period of time to purge the fuel vapor. Nevertheless, it is undesirable to employ a technology for solving this problem that would negatively impact the fuel economy of the engine.